烧结-硬化钢的尺寸精度

尺寸精度是铁基粉末冶金零件生产工艺的关键参数.除了和标准粉末冶金低合金钢的压制与烧结相关的尺寸变化外,烧结-硬化合金还会产生从奥氏体转变为马氏体的相变.马氏体是钢中密度最低的相,因此,冷却时马氏体的形成会导致零件显著胀大.当马氏体转变为密度较高的铁素体与碳化物显微组织时,回火的淬硬钢发生收缩.这两种相变对零件的尺寸变化都有很大影响.另外,在Cu与C含量高的马氏体区可能有大量残余奥氏体存在.奥氏体相密度最高,所以残余奥氏体会导致压坯胀大较小.除回火处理外,马氏体与残余奥氏体的存在都会影响零件的最终尺寸.本文考察了两个烧结-硬化钢牌号,同时通过不同的后烧结热处理,研究了这两个牌号钢的尺寸变化和显微组织变化.

Dimensional precision in sinter-hardening PM steels

Dimensional precision is a critical parameter in net shape processing of ferrous PM components.Beyond the dimensional changes associated with pressing and sintering of typical low alloy PM steels,sinter-hardening alloys undergo a transformation from austenite to martensite.The formation of martensite results in a large expansion during cooling,as martensite is the lowest density phase in steels.Tempering hardened steels results in shrinkage,as the martensite converts to a ferrite and carbide microstructure ...